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cmd/compile: constant-fold switches early in compilation

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So that the inliner knows all the other cases are dead and doesn't
accumulate any cost for them.

The canonical case for this is switching on runtime.GOOS, which occurs
several places in the stdlib.

Fixes 

Change-Id: I44823aaebb6c1b03c9b0c12d10086db81954350f
Reviewed-on: https://go-review.googlesource.com/c/go/+/399694
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Keith Randall
2022-02-06 23:25:04 -08:00
parent 1ba96d8c09
commit 01b9ae22ed
2 changed files with 125 additions and 0 deletions
src/cmd/compile/internal/deadcode
deadcode.go
test
inline.go

45
test/inline.go

@ -160,6 +160,51 @@ func switchType(x interface{}) int { // ERROR "can inline switchType" "x does no
}
}
// Test that switches on constant things, with constant cases, only cost anything for
// the case that matches. See issue 50253.
func switchConst1(p func(string)) { // ERROR "can inline switchConst" "p does not escape"
const c = 1
switch c {
case 0:
p("zero")
case 1:
p("one")
case 2:
p("two")
default:
p("other")
}
}
func switchConst2() string { // ERROR "can inline switchConst2"
switch runtime.GOOS {
case "linux":
return "Leenooks"
case "windows":
return "Windoze"
case "darwin":
return "MackBone"
case "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "100":
return "Numbers"
default:
return "oh nose!"
}
}
func switchConst3() string { // ERROR "can inline switchConst3"
switch runtime.GOOS {
case "Linux":
panic("Linux")
case "Windows":
panic("Windows")
case "Darwin":
panic("Darwin")
case "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "100":
panic("Numbers")
default:
return "oh nose!"
}
}
func inlineRangeIntoMe(data []int) { // ERROR "can inline inlineRangeIntoMe" "data does not escape"
rangeFunc(data, 12) // ERROR "inlining call to rangeFunc"
}